1. Field of the Invention
The present invention relates to thermometers and more particularly, to a pre-heat type clinical thermometer that preheats the sensor tip of the thermometer so that measurement of the temperature of a human body can be done quickly and accurately.
2. Description of the Related Art
Many pre-heat type clinical thermometers are known. Exemplars are seen in U.S. Pat. No. 6,109,784 entitled “FAST RESPONSE DIGITAL THERMOMETER” and U.S. Pat. No. 6,250,802 entitled “ELECTRONIC THERMOMETER WITH PREHEATING”. These prior art designs use the internal battery to pre-heat the sensor tip so as to shorten the measuring time.
However, the pre-heating method of using a battery to pre-heat the sensor tip has the following drawbacks:
1. The power capacity of the internal battery of the thermometer is limited, using the internal battery to pre-heat the sensor tip consumes much the battery power and takes much time.
2. Before use, it is necessary to turn on the pre-heat function, and a waiting time is necessary before finish of the pre-heat function.
3. The pre-heat function simply pre-heats the sensor tip to the normal human body temperature range about 35° C.˜37° C. Before the person to be measured is moved to the measuring position and the thermometer is attached to the selected part of the body of the person, the thermal energy may be dissipated from the sensor tip and the temperature of the sensor tip may be lowered, unable to effectively raise the measuring speed.
4. The heating wire of the pre-heat circuit extends to the deep inside of the sensor tip, increasing the heat capacity, and therefore the measuring time is relatively prolonged.
There is known another prior art pre-heat type clinical thermometer that uses a pre-heat box to heat the sensor tip of the thermometer directly. This design achieves rapid pre-heating of the sensor tip. However, when the user takes the thermometer out of the pre-heat box, the temperature of the sensor tip may drop rapidly due to the effect of the cold outside open air.